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Every fence and deck footing starts with a hole about three times the post's width and, for fences, about a third of the post's height deep — deeper where frost lines demand it. A manual clamshell digger handles a few holes in soft soil; a powered auger pays off on long fences, while a digging bar is what gets you through rock and roots either way.
Count your holes with the fence post concrete calculator or the deck footing calculator, then choose below. This guide compares types by specification; it is not a hands-on product test.
Pros and cons describe each type from its specifications; this is not a hands-on product test. As an Amazon Associate we earn from qualifying purchases.
Best for: Up to about a dozen holes in soft or loamy soil. Check: Fibreglass or steel handles and a blade wide enough for your hole size.
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Cons
Best for: Long fences and many deck footings. Check: Engine size, bit diameters included, and a two-person or one-person frame.
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Cons
Best for: Medium jobs and gardens where noise and fumes matter. Check: Torque rating, bit diameter and depth, and battery capacity.
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Best for: Breaking rock, cutting roots and tamping backfill. Check: Length (5 to 6 ft), weight, and a chisel point plus tamping end.
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Worked example: A 150 ft wood fence with one gate, posts 8 ft apart
22 holes and about 30 cu ft of soil — a job where a powered auger (bought or rented) usually earns its keep.
Run your own fence through the wood fence calculator for posts, rails, pickets and concrete in one list.
| Soil | Best choice | Notes |
|---|---|---|
| Loam or sand | Clamshell or any auger | Sand caves in — dig, set and pour the same day |
| Clay | Gas auger, then clamshell | Wet clay sticks to bits; lift the bit often |
| Rocky | Digging bar plus clamshell | Augers kick on rock; break it out first |
| Roots | Digging bar or a pruning saw | Cut roots before the auger catches them |
| Frozen | Wait, or rent a hydraulic auger | Frozen ground is not worth fighting by hand |
A powered auger for clay, used with a digging bar to break out rocks and cut roots; a clamshell digger then cleans out the hole. In heavy rock, rent a hydraulic or tow-behind auger.
For more than about 15 to 20 holes, usually yes — or rent one for a day. For a handful of holes in soft soil, a manual clamshell digger is cheaper and quieter.
A common rule is a third of the post's height above ground, plus a few inches of gravel, and below your local frost line. Many 6 ft fences use holes about 30 in deep.
About three times the post's width: roughly 10 to 12 in for a 4x4 and 14 to 18 in for a 6x6. Deck footings follow the size your plans or local code call for.
Yes, in soft to medium soil with the right bit size. Check the torque rating and battery capacity; for wide holes in clay, a gas auger has more power.